Asynchronous transfer mode (ATM) is now well recognized as the fundamental switching and multiplexing technique for future broadband ISDN. As these networks will be increasingly relied upon for providing a multitude of integrated voice, data, and video services, network reliability is a key concern. There are several intrinsic features of ATM networks that could potentially be exploited to provide improved restoration techniques, beyond those established for synchronous transfer mode (STM) networks, such as digital cross-connect restoration or self-healing rings. These features include ATM cell level error detection, inherent rate adaptation and nonhierarchical multiplexing. The authors explore the use of these features in developing fast restoration strategies for ATM networks. In particular, they address: (1) ATM error detection capabilities for enhanced failure detection, (2) network rerouting strategies, (3) spare capacity allocation, and (4) network control architecture and related implementation aspects. Their findings suggest that fast network span failure detection and bandwidth-efficient rerouting capabilities can be combined to develop restoration strategies for ATM networks with significantly greater performance-cost ratios when compared to existing STM network restoration strategies. >

Fast restoration of ATM networks

Distributed path restoration based on optical cross-connects can provide highly capacity-efficient real-time restoration for WDM-based optical networking. However, to obtain an assured restoration level with the theoretically very low amounts of spare capacity that path restoration allows, one must solve, or closely approximate a solution to, the integer multicommodity maximum flow (MCMF) problem, MCMF is, however a hard combinatorial optimization problem due to what is called the "mutual capacity" aspects of the problem: which of many competing origin-destination pairs should be allowed paths over the finite spares on each span? Integer MCMF is further complicated by the nonunimodular nature of the problem, i.e., fractional flows are forbidden but would arise if solved by linear programming. This paper presents a heuristic principle that tests well against integer programming solutions of MCMF routing. The heuristic is first characterized in a centralized program, then adapted for use in a distributed path restoration protocol. In all test cases, the protocol obtains over 97% of the paths found in an optimal MCMF solution in the same network. Via OPNET simulation it is also predicted that the protocol will run in well under 2 seconds which means it could be used directly in real-time, or in distributed prefailure self-planning, for restoration. The significance is that network operators could aggressively optimize their spare capacity, toward theoretical minimums, while still assuring 100% restorability.

http://www.ece.ualberta.ca/~grover/pdf/Path_rest_%20DRA_JSAC.pdf

A highly efficient path-restoration protocol for management of optical network transport integrity

Fast restoration of broadband optical fiber networks from multiple-link and node failures, as well as single-link failures, is addressed. A distributed restoration algorithm based on message flooding is described. The algorithm is an extension of a previously proposed algorithm for single-link failure. It restores the network from multiple-link and node failures, using multidestination flooding and path route monitoring. Computer simulation of the algorithm verified that it can find alternate paths within 0.5 s, whenever the message processing delay at a node is 5 ms. >

A distributed restoration algorithm for multiple-link and node failures of transport networks

A restoration system is provided for enhancing the reliability of a telecommunications network such that particular traffic which is disrupted by, for example, a faulty link, may be quickly rerouted via an alternate route established "on the fly". In particular, each node and link forming the network is monitored, and in the event that such monitoring detects a faulty link or node then a central controller is notified. The controller is arranged to locate spare capacity and establish an alternate route, in which the continuity of the alternate route is confirmed before the disrupted traffic is transferred thereto.

Telecommunications network restoration architecture

A Growing Dependency The Disrupters Are Among Us Asleep at the Switch Protecting Your Information Assets Protection Posture Case Studies Summary and Conclusions Appendices References Glossary Index.

Protection and Security on the Information Superhighway

Modern telecommunications network design and examples of possible causes of service interruption are examined, using AT&T 800 Service for illustration. Different methods of assuring service technically are presented. It is shown how end-to-end service reliability can be improved by using the techniques described, applying them to 800 Service as an example. Techniques used to restore generic switched services or private line services after a failure within a network are also presented. >

W.E. Falconer

Papers

Service assurance in modern telecommunications networks